The present invention provides for a lightweight helicopter that is simple to operate and affordable for individuals or groups for purposes of aerosports and hobby flying. While a number of affordable aircraft, such as micro-lights and powered hang gliders, have brought the possibilities of powered flight within the reach of the public and lead to an upsurge in aerosports, the same is not true of the helicopter. The helicopter remains an expensive machine to acquire and difficult to learn to operate and to fly safely.
For example, a single seater powered hand glider manufactured in the Republic of India is available for about $4,500 (Rs. 2.0 lakhs) and requires about 10–15 hours instruction before an average person can fly solo. On the other hand, a recently introduced single seater ultralight helicopter, for example the Ultrasport 254 (American Sportscopter International Inc., Newport News, Va.) costs around $35,000 (Rs. 15 lakhs) in a kit form. The helicopter requires expensive training in a similar two-seat helicopter, which may require 100 hours and cost $13,700–$18,300 (Rs. 6–8 lakhs) for the training. This difference arises mainly due to the increased complexity of a conventional helicopter, which results in an expensive machine that is difficult to learn to fly. However, the ability of a helicopter for vertical as well as forward movement, makes it very attractive as a flying machine and would certainly prove to be very popular if made simple to fly and affordable.
Reference may be made to U.S. Pat. No. 5,370,341 issued Dec. 6, 1994 and entitled ultra-light helicopter and control system, which is hereby incorporated by reference as if fully set forth herein. The '341 patent consists of an ultra light helicopter with a pair of counter-rotating rotor assemblies. The pilot is suspended in a supine position in a hang glider type harness under the rotors. The pilot holds a control bar fixed to a frame and maneuvers the helicopter in pitch and roll directions by manipulating the control bar which results in the shift of his center of gravity relative to the center of gravity of the helicopter, thereby tilting the thrust axis of the rotors resulting in the maneuvering of the helicopter. The pilot also operates the engine throttle and pitch control mechanism of the rotor bladders with twist-grips formed on the control bar. With this control, he can control the vertical movement of the aircraft.
This invention has several drawbacks. One drawback being that the pilot is freely suspended in a prone position (i.e, face downward) under the downwash of the rotors, which is likely to lead to large swaying and buffeting of the pilot making it difficult to control the aircraft. In another drawback, the prone position is also considered to be extremely dangerous from a crash-worthiness point of view. In an additional drawback, the absence of a positive control in the yaw direction in hover and low forward speeds could lead to undesirable spinning of the pilot about a vertical axis. It appears very difficult to introduce any further controls to overcome this problem, since both the hands of the pilot are fully occupied in manipulating the control bar, the rotor blade pitch control and the engine throttle and the pilots' feet are not available to carry out any control function because of the prone freely hanging position.
The use of two counter-rotating rotors is employed in some helicopters, such as for example, a Kamov helicopter of Russian origin and reported in Janes “Aircraft of the World.” The use of counter-rotating concentric rotors has the advantage of having a zero net angular momentum thus avoiding the requirement of a tail rotor for torque balancing required in the single main rotor arrangement, as in the conventional helicopters. There is also a saving in power, which is normally consumed by the tail rotor of a conventional helicopter. However, due to the lower rotor being placed in the wake of the upper rotor, there is an interference effect, which results in an increase in the power required for a given thrust, thus nullifying to some extent, the savings in power of the tail rotor.
Another feature of the Kamov concentric contra-rotating rotors is the use of differential pitch control of the two rotors for achieving control in the yaw direction. This machine therefore needs a collective pitch, a cyclic pitch and differential pitch arrangements for its control. With all these features, the mechanical complexity is very high, leading to an expensive and complex machine.
We can estimate the size of the rotors based on the disk loading and power loading of lightweight machines in a similar class. With reference to FIG. 5, a plot is shown of these parameters for five helicopters. It would appear that ROSS-1 from '341 patent could turn out to be somewhat underpowered. HT-1 (1) and HT-1 (2) are present designs, one fitted with a 42-hp Rotax 477-2V engine and a 50 hp, Rotax 503-2V engine respectively. The weight estimates for each aircraft design indicates that the HT-1 (1) would weigh about 115 kg and HT-1 (2) would weigh about 127 kg. Thus, the HT-1 (1) could achieve the ultra-light category but it may be somewhat underpowered and the HT-1 (2) could have sufficient power but would not meet the ultra-light category weight limit.